A Lunar Telescope Will Reveal the Shadows of Distant Black Holes express
The farther apart the antennas, the finer the details they pick up. By merging signals, astronomers effectively turn multiple dishes into a single telescope as big as the distance between them. Add a lunar antenna to the Earth-based array, and you get a virtual eye 384 000 km wide. It's like looking at the cosmos through the eyes of a giant, with pupils set an Earth–Moon span apart.
The real showstopper is the photon ring. This is an ultra-thin rim of light, forged by extreme spacetime curvature. To make it out, we'll need additional antennas drifting in the void between Earth and the Moon. Then black hole shadows will snap into sharp focus, letting us test gravity where it's pushed to its limits.
Original abstract
as written by the authors arXiv:2601.02812v2
The 1.3 mm ground-based very long baseline interferometry (VLBI) array Event Horizon Telescope (EHT), is limited by Earth's diameter, restricting its black hole shadow imaging to only M87* and Sgr A*. Extending baselines to the Moon would achieve ~0.7 uas angular resolution at 230 GHz, enabling shadow detection for a much larger sample of supermassive black holes (SMBHs). The concept is motivated by space VLBI missions and lunar exploration, including the ongoing Lunar Orbit VLBI EXperiment (LOVEX) aboard QueQiao-2 (Chang'E-7) and the planned International Lunar Research Station (ILRS). We assess shadow detectability for 31 SMBHs with predicted large angular sizes, exploring different telescope location and antenna size. Assuming a telescope at the lunar antipode, we simulate the Moon-Earth (u,v) coverage and show that sources with direction near the Moon's orbital plane yield projected baselines spanning from short to long, enabling sampling of the first visibility null - a key shadow signature. Using a geometric ring model, we identify six shadow-detectable candidates for Moon-Earth VLBI. Among these, M104, NGC 5077, and NGC 1052 are detectable with a 5 m lunar-based telescope; PGC 049940 requires 10 m; NGC 524 requires 20 m; and NGC 5252 requires 40 m. Furthermore, if space telescopes fill the baseline coverage gaps between Moon and Earth, the n=2 photon ring region is detectable for Sgr A*, M87* with a 10 m lunar-based telescope, and 12 candidates are detectable for the n=1 photon ring region using a lunar-based telescope of up to 40 m. These results provide a clear scientific and technical motivation for lunar-based telescopes in future black hole shadow studies.
The system's angular resolution—0.7 microarcseconds — is like spotting an orange left on the Moon’s surface while standing on Earth.
Like in Interstellar, but even crisper: the lunar telescope promises to show black hole shadows with Hollywood-level detail.